This invention relates to an arrangement for detecting/inspecting items prior to them being packaged, and has particular application to pharmaceutical items, such as tablets, pills, capsules and the like.
Item inspection arrangements, for example for inspecting tablets to establish if they are whole or broken to some degree, are known which utilise the passage of the tablets between two plates of a single capacitor. This results in a change of capacitance and a corresponding signal which is processed to provide an indication of the result of each inspection.
It has however been established that an item 1 having a rectangular plan, when disposed between parallel capacitor plates 2, 3, produces a varying increase in capacitance as it is rotated about a vertical axis (FIG. 1). Since the orientation of the item in space is random, there is a large error resulting from orientation. A secondary further effect disrupting the inspection is the xe2x80x98endxe2x80x99 effect, which reduces field density at the mid-point between the capacitor plates, compared to that nearer each plate. Accordingly the sensitivity to an item varies as the item is moved along a line perpendicular to the plates.
An object is to minimise or obviate these disadvantages by providing an improved detection/inspection arrangement.
An item detection/inspection arrangement of the invention comprises at least four capacitor plates arranged together in at least two pairs of opposing or generally opposing plates to provide, in use, at least two intersecting electric fields, items passing through said fields, in use, producing respective signals/pulses dependent on the changes of capacitance for the pairs of plates, and processing means for producing from said signals/pulses, detection/inspection data for said items.
As used herein, the reference to electric(al) fields xe2x80x98intersectingxe2x80x99 includes actual intersection i.e. by two or more fields which are together simultaneously in existence, and also spacial intersection, i.e. where the fields do not exist together at any time but, when they exist separately, are positioned in space (within the transducer) so that they would intersect if they did exist simultaneously. Accordingly it will be appreciated that the invention relates not only to the spacial intersections of the second embodiment described, where the plates are sequentially pulsed, but also to actual intersecting electric(al) fields as is the case with the first embodiment where the two pairs of plates are driven not in phase.